1. Field of the Invention
The present invention relates to a photoelectric sensor capable of detecting a desired workpiece by comparing a received light quantity with a threshold value, and a photoelectric sensor system configured by coupling a plurality of such photoelectric sensors.
2. Description of Related Art
A photoelectric sensor typically projects light to a detection area and receives light from the detection area, and compares a quantity of the received light with a predetermined threshold value, thereby detecting the presence of a workpiece in the detection area. As one aspect of this type of photoelectric sensors, there has been known a photoelectric sensor system in which a plurality of such photoelectric sensors are coupled and light is projected to plurality of portions, thereby monitoring a condition of a workpiece.
Such a photoelectric sensor includes a light-emitting device such as an LED or a laser diode and a light-receiving device such as a photodiode that are built-in. The commonly used photoelectric sensors inevitably show variation in luminance of the light-emitting devices and variation in sensitivity and offset of the light-receiving devices, and such. Further, in the case of the photoelectric sensors of a type in which an optical fiber is inserted and light is guided using the optical fiber, variation in light coupling efficiency is also shown due to variation in insertion of the optical fibers. As a result of these variations among the individual sensors, even when the plurality of photoelectric sensors are used under the same environment, quantities of the received light obtained by the respective photoelectric sensors do not become completely the same.
If the received light quantity obtained for each photoelectric sensor is different from sensor to sensor, it is necessary to set a threshold value that corresponds to a characteristic of each photoelectric sensor, resulting in a lot of trouble for a user. In addition, if the displayed received light quantity is different from sensor to sensor even though the photoelectric sensors are used under the same environment, this can possibly undermine the user's confidence in the system.
At the same time, there has conventionally been known a scaling function for scaling the received light quantities to display. The scaling function is for adjusting a received light quantity to a previously set scaling target value and displaying a received light quantity that is obtained subsequently by scaling up or down based on a scaling adjustment ratio (see Japanese Unexamined Patent Application Publication No. 2007-158497, for example). Known examples of the scaling function include a technique that the light-emitting device and the light-receiving device are controlled such that an actually obtained received light quantity becomes closer to a scaling target value, or that an actually obtained received light quantity is not changed and a displayed value of the received light quantity is displayed by scaling up or down.
By executing the scaling function, it is easily possible to set the received light quantities of the plurality of photoelectric sensors to be displayed as an identical value. Accordingly, it is possible to manage the threshold value of the plurality of photoelectric sensors in an integrated manner, as well as to improve the way in which the display of the received light quantities look for the user.